Coated fabrics and methods for applying coatings thereto

ABSTRACT

Glass fibers in the form of yarns and fabrics are provided with a surface treatment to improve their resistance to abrasion and flammability by coating the yarns and fabrics with a thickened dispersion of very fine particles of a solid organic polymeric material, drying and sintering this coating through various heating zones, and optionally padding the treated yarns and fabric with a lubricant to ensure flexibility thereof.

United States Patent Dillon [45] Apr. 4, 1972 [54] COATED FABRICS ANDMETHODS FOR APPLYING COATINGS THERETO [72] Inventor: James J. Dillon,Providence, R1.

[73] Assignee: Owens-Corning Fiberglas Corporation [22] Filed: Sept. 5,1969 21 Appl. No.: 855,513

2,712,509 7/l955 Biefeld ..28/75 R 2,731,367 1/1956 Caroselli. 17/126 GS2,754,223 7/1956 Caroselli.... 17/126 GB 2,907,677 10/1959 Hochberg..17/126 GB 3,434,875 3/1959 Smith et al. ..l17/126 GS PrimaryExaminer-William D. Martin Assistant ExaminerD. Cohen Attorney-Statelin& Overman and Robert E. Witt [57] ABSTRACT Glass fibers in the form ofyarns and fabrics are provided with a surface treatment to improve theirresistance to abrasion and flammability by coating the yarns and fabricswith a thickened dispersion of very fine particles of a solid organicpolymeric material, drying and sintering this coating through variousheating zones, and optionally padding the treated yarns and fabric witha lubricant to ensure flexibility thereof.

5 Claims, 2 Drawing Figures Patented April 4, 1972 3,653,949

' INVENTOR.

(/4145; J 5/4 1 av COATED FABRICS AND METHODS FOR APPLYING COATINGSTl-IERETO The invention described herein was made in the performance ofwork under a NASA contract and is subject to the provisions of section305 of the National Aeronautics and Space Act of l958, Public Law 85 568(72 Statute 435; 42 U.

This invention relates to glass fibers characterized by a markedincrease in resistance to deterioration by abrasion and it relates moreparticularly to glass fiber fabrics having improved abrasion andflammability resistance and to a method and composition for use in thepreparation of the same.

Glass fibers are employed extensively in the manufacture of fabrics ofhigh strength, high resistance to wrinkling, good washability, excellentappearance, and in which one or more of the important characteristics isresistance to heat and flammability. One of the barriers to the morewidespread usage of glass fibers as a textile material resides in therelatively low abrasion resistance of the glass fibers whereby thefibers fray or break down in response to mutual abrasion or othersurface abrasions to which the glass fiber fabric might be exposedduring use.

Substantial inroads have been made in overcomingthe relatively poorabrasion resistance of the glass fibers and fabrics formed thereofwhereby glass fiber fabrics have found increased utilization as atextilematerial in applications where 'fire resistance, strength, wrinkleproofness, flexibility and appearance constitute one or more of thefactors in the selection of a textile material.

Because of the many outstanding properties ofglass fibers as a textilematerial, extensive research and development has been expended towardsthe further increase of the abrasion resistance of glass fibers andfabrics formed thereof, and in the same regard to maintain or furtherincrease the fire resistance properties of glass fibers and fabricsformed thereof.

It is an object of this invention to provide a method for producingglass fibers and fabrics formed thereof having greatly improvedresistance to abrasion and greatlyimproved resistance to flammability,in which the improved properties are achieved without loss of otherdesirable properties possessed by glass fibers or fabrics formedthereof.

It is another object of this invention to provide a method andcomposition for use in the treatment of glass fibers and fabrics formedthereof whereby the same are highly resistant to deterioration by mutualor other abrasion and are self extinguishing in an oxygen atmosphere andit is a related object to provide a treatment of the type describedwhich makes use of relatively low cost and readily available materials;which can be applied in a simple and efficient manner during theprocessing of the fibers and fabrics formedthereof; which does notinterfere with the processing of the glass fibers during formation ofthe glass fiber filaments in yarns, cords and fabrics formed thereof;which does not interfere with the fuller utilization of the desirableproperties of the glass fibers and glass fiber fabrics and which resultsin a glass fiber fabric of high strength, good appearance and long life.

These and other objects and advantages of this invention willhereinafter appear, and for purposes ofillustration but not oflimitation embodiments of the invention are shown in the accompanyingdrawings, in which FIG. I is a schematic view showing the arrangement ofelements for the treatment of glass fibers in conjunction with a glassfiber forming operation, and

FIG. 2 is an enlarged sectional view across a woven glass fiber fabrictreated in accordance with the practice of this invention.

Continuous glass fiber filaments are formed by rapid attenuation ofmolten streams of glass 12 issuing from hundreds of orifices in thebottom side of a glass melting furnace 14. The bare surfaces of theformed glass fiber filaments are wet at a coating station 16 with aconventional sizing composition. Application to the individual filamentsmay be made by means of a roller coater 18 schematically illustrated inFIG. 1, in position to engage the glass fiber filaments before they arebrought together to form a glass fiber bundle 20. The roller makescontact with a reservoir of the coating composition whereby the surfacesof the roller become wet for transfer to the filaments as they passthereover. The sized filaments are subsequently gathered together in theform of a strand or bundle and wound upon a rapidly rotating collet ordrum 22 which operates to pull the fibers to effect the describedattenuation. The treated strands can thereafter be twisted and plyedinto yarns and woven into fabric and then treated by the inventiveconcept. However, the treated strands can be further subjected toadditional finishing operations. in accordance with the inventiveconcept, prior to beingwoven into fabric.

It has been found that the abrasion resistance and selfextinguishingcharacteristics of theftreated glass fibers or fabric formed thereof inan oxygen atmosphere can be increased many fold when they are coatedwith a thickened dispersion of polytetrafluoroethylene. The thickeneddispersion is applied to glass fibers and fabrics formed thereofpreferably prior to any heat cleaning of the fibers or fabrics, i.e. thedispersion is applied to greige yarns and fabrics. By coating the glassfiber yarns andfabrics prior to heat cleaning, only one heat cycle isrequired to burn off or expel unwanted volatiles and to obtain a uniformcoating of the polytetrafluoroethylene thereon.

It has been observed thatby first heat cleaning the yarns or fabricsprior to coating thesame with the thickened dispersion and subsequentlyexposing the same to another heat cycle, other desirable properties andcharacteristics of the glass fibers, especially the strength properties,are adversly affected.

When the glass fibers or fabric are treated according to the inventiveconcept three objects are accomplished: l organic matter or volatilesare distilled off; (2) the polytetrafluoroethylene is sintered slowly;and (3) when the glass fibers are in fabric form the fabric is heat set,i.e. a permanent crimp is established in the glass fibers of the fabricto help give dimensional stability thereto. Furthermore, when thevolatiles are distilled off by the inventive concept hereinafterdescribed in *greater detail the fabric remains very white in color.

It was observed during the development of this invention that when theyarns are twisted and subsequently coated with polytetrafluoroethyleneand exposed to high temperatures ranging up to 750F. for periods up to 1minute the resultant yarn is brown in color, probablybecause not all ofthe organic material has had a chance to be expelled, thereby making thetreated yarns susceptible to flammability in an oxygen atmosphere.Furthermore the treated yarn may have bumpy characteristics due to anuneven flow of the polytetrafluoroethylene coating thereby makingsubsequent weaving operations difficult and inefficient. From this observation it was determined that a gradual build up of temperature over anextended time period would be desirable in order to overcome the abovedeficiencies.

The inventive process is applied to glass fibers that have been twistedand/or plied into yarns, wherein the fibers have a forming size thereon.A dispersion of polytetrafiuoroethylene is subsequently coated onto theyarns arid the coated yarns are merely dried so that the coating on theyarns is not immediate ly melted nor sintered. This is accomplished byheating the coated yarns at a temperature of from 300 to 350 F. forpreferably 30 seconds to 5 minutes, however exposure of up to 24 hourswill not adversely affect the properties. This dried yarn is then woveninto fabric form and the fabric is subsequently heat cleaned to expelvolatile organic materials therefrom and at the same time to make thepolytetrafluoroethylene flow, and to weave set the yarns in the fabricthereby yielding a smooth, uniform coating on the fabric. With thisprocess, it has been noticed that (1) this yields an efficient coatirtgoperation of the yarns, and (2) the coating is smooth and uniform foreasy harlcllirig and further operations, and when woven into fabric formand heat treated, the fabric possesses good hand, flexibility, strength,and is white in color. Additionally, subsequent to heat cleaning, a

lubricant may be padded on the fabric to insure or increase flexibilitythereof. The lubricant may be an organosilicon compound selected fromthe group consisting of a silane, its hydrolysis product, and itspolymerization product wherein the silane has from one to three highlyhydrolyzable groups attached to the silicon atom and at least oneorganic group attached to the silicon atom. The organosilicon compoundshould be applied to the treated glass fiber surfaces in a very dilutesolution or dispersion in an aqueous medium or in organic solventscontaining less than 2 percent by weight of the organosilicon compoundsufficient to form at least a monomolecular layer. An example of such anorganosilicon compound is XEC-4-2l02 commercially available from theDow-Corning Corporation.

Other lubricants that may be suitably used are cationic softeners, suchas quarternary ammonium salts of amides or imidazolines and acetatesalts of tetraethylene pentamine mono-, di-, poly-stearate, or non-ionicsofteners such as polyethylene dispersions or emulsions, glycerinemonostearates and amino and imide derivatives of high molecular weightfatty alcohols. Also, chromium complexes, such as stearato chromicchloride, and methacrylato chromic chloride have been found to maintainthe flexibility of fabrics treated in accordance with the inventiveconcepts.

Advantages possessed by the yarns and fabrics treated by the concepts ofthe subject invention include; (1) their whiteness, (2) their hightensile properties, (3) their high abrasion resistance, (4) theirexcellent flexibility and hand, and (5) their non-flammability, even inan oxygen atmosphere at 16 psia.

It was further observed that when techniques other than the inventiveconcept were employed to apply a polytetrafluoroethylene dispersion togreige glass fabric, such as by impregnation, serious drawbacksdeveloped, i.e. a dirty brown color appeared on the fabric after ovendrying and sintering and the fabric was stiff and its resistance toflammability was adversely affected.

Fabrics treated by the inventive concept find increased utility inapplications where protective clothing is necessitated, i.e. protectionfrom heat, fire and chemicals.

Other materials other than polytetrafluoroethylene that are suitable tocoat glass fiber fabrics by the inventive concept are KEL-F andFluorels, polyflorinated polymers manufactured by the Minnesota MiningCompany. These above materials also appear to provide increased wrinklerecovery and better hand to the treated fabrics.

A commercially available polytetrafluoroethylene (Teflon 30) dispersionwas thickened with commonly known thickening agents such as Carbopol,Methocel, and Superclear (natural or synthetic gum or modificationsthereof).

Knife coating the thickened polytetrafluoroethylene dispersion onto theglass fiber fabrics is accomplished with a knifeover roll, floatingknife, reverse roller or other suitable means. When thepolytetrafluoroethylene is applied to a glass fiber yarn, a wiping die,wiping rod, or dip coating is sufficient to apply the coating thereon.

By controlling the time and temperature that the coated yarns or fabricsare exposed to, caramelization or brownish color is avoided on the yarnsor fabrics because all of the organic volatile materials are distilledoff. A suitable method for accomplishing this follows. The thickenedpolytetrafluoroethylene dispersion is coated onto glass yarn or glassfabric at room temperature. The amount of polytetrafluoroethyleneapplied to the glass yarn or the glass fabric is dependent upon thedesired properties and end uses of the glass yarns and fabric. Forexample, if the treated glass fabric is to be used as protectiveclothing wherein the fabric is exposed to dynamic use a lesser amount isapplied than if it is to be used in a static situation such as a wallcurtain. However, amounts of polytetrafluoroethylene in the range offrom about 0.5 to about 40,0 percent by weight per weight of the fabricis sufficient. Preferably, when glass fabric is coated, the amount ofpolytetrafluoroethylene is from about-2.0 to about 15.0 percent byweight per weight of the fabric for each surface of the fabric.Depending upon the end use of the treated fabric, it is usuallypreferred to coat only one surface of the fabric. Subsequently thecoated yarns woven into fabric, or coated fabrics are exposed totemperatures ranging from 300-750" F. over a period ranging from 12-60hours. This temperature range has been determined to be that at whichthe volatiles distil off the coated yarns or fabrics without exothermicdecomposition. At this temperature range sintering of thepolytetrafluoroethylene, and weave setting and heat cleaning of theyarns and fabric occur simultaneously.

When thickeners are added to a commercially availablepolytetrafluoroethylene dispersion its consistency or viscosity shouldbe suitable for knife coating, or other conventional means for coating.The amount of thickener that is added to the polytetrafluoroethylenedispersion ranges from about 10 to about 60 percent by weight, ofa 3-5percent aqueous solution of solids, per weight ofpolytetrafluoroethylene dispersion.

Organic solids, present in forming sizes etc.', when not given a chanceto escape during the heat treatment, caramelize or turn the fabric anundesirable brown color and impair its nonflammability properties.Furthermore, if the fabric is exposed to a padding operation or isimpregnated with the polytetrafluoroethylene dispersion there is a morecomplete coating of the internal fibers making up the body of the yarnsthereby inducing caramelization, and on flexing, the fabric cracks andcrazes. Cracking and crazing of the fabric finish adversely affects thepurpose of the inventive concept, i.e. to improve abrasion resistance,fire resistance, hand, et al.

Any fusing of the polytetrafluoroethylene coating that occurs at theyarn cross-over points in a woven fabric, formed by the intersection ofwarp and fill yarns, during the heat treatment process may be eliminatedby flexing or washing the fabric, without deleteriously affecting thefabric finish.

Having described the basic concepts of this invention and thetheoretical considerations believed to be involved, illustrations willnow be made of the practice of this invention.

EXAMPLE I [n the following example, the inventive treatment is carriedout with fabrics woven ofglass yarns in which glass fibers making upthese yarns have previously been sized with a conventional sizecomposition in the forming operation to enable the fibers to beprocessed into strands, yarns, and fabrics and in which the originalsize has not been removed from the fabric by conventional means such asby washing or by burning off in response to heating the fabric in anoxidizing atmosphere.

A woven fabric 28 as pictured in FIG. 2 is produced by subjecting it toa knife coating operation with a thickened polytetrafluoroethyleneaqueous dispersion 34 having a consistency suitable for knife coating,i.e. analogous to the thickness of whipped cream. Knife coating only onesurface of the fabric increases flexibility and hand because there is nointerlocking of the yarns Warp yarns 32 and fill yarns 30 are generallynot bonded together such as by fusing, but any fusing that may occur atthe cross-over points 36 of the warp and fill yarns may be subsequentlyeliminated by flexing the fabric, without deleteriously affecting thefinish.

The treated fabric is placed in an oven at room temperature wherein gasburners are subsequently turned on in order to controllably reach atemperature ranging from 300-750 F. The controlled build-up oftemperature is a necessary feature so that the volatiles will not belocked therein. The tempera ture should increase from room temperatureto about 450 F. slowly (5-30 minutes) and held at the latter temperaturefor a period ranging from 1 to 15 hours. The volatile organic materialsdistil off without exothermic decomposition. Subsequently thetemperature is slowly raised (over a 30 minute period) to about 650-750F. and held for an additional 15-35 hours at which temperature sinteringof the polytetrafluoroethylene and heat cleaning and weave setting ofthe fabric occurs.

The heat treated fabric is white in color, shows excellent strengthproperties, shows that it is self-extinguishing in an oxygen atmosphereup to 16.5 psia and furthermore possesses good flexibility and hand.

EXAMPLE 11 Glass yams previously treated with a protective sizing werecoated with a thickened aqueous dispersion of polytetrafluoroethylene bymeans of a wiping die. Subsequently, the yarns were dried and woven intofabric. The treated fabric was exposed to a heat cycle wherein thetemperature was slowly increased from room temperature to about 400-500F. and held at the latter temperature fro about 5 hours. Subsequentlythe temperature was increased to about 750 F. and held there for anadditional hours, in order to heat clean and weave set the fabric and tosinter the polytetrafluoroethylene thereon. Optionally, the fabric wastreated with an aqueous solution of an organo silicon, such as XEC4-l02, manufactured by the Dow-Corning Corporatron.

EXAMPLE Ill Glass yarns, treated with a protective sizing but not heatcleaned, were coated with a thickened aqueous dispersion ofpolytetrafluoroethylene by means of squeeze pads and subsequently driedvery slowly at a temperature of about 350 F. for about 1 hour. The glassyarns with the dried coating thereon were then sintered at a temperatureof about 65070 0 F. for about 12 hours in order to obtain a uniform filmof polytetrafiuoroethylene thereon and to distill off unwanted volatilesfrom the yarns.

Thereafter the treated yarns were collected on a drum for shipping toweavers for fabrication into fabric. Some of the treated yarns werewoven into fabric, and the fabric was optionally heat cleaned in orderto achieve some weave setting of the yarns within the fabric.

When glass yarns are treated with a aqueous dispersion ofpolytetrafluoroethylene, the dispersion may be thickened or unthickened,depending upon the method of application to the glass fibers and theintended end-use of the treated fibers.

lclaim:

l. A method for improving abrasion resistance and flammabilityresistance of glass fabric, said glass fabric comprising glass fibers inthe form of bundles, said bundles comprising a multiplicity of the glassfibers sized with a protective material, comprising the steps ofapplying a thickened dispersion of very fine particles of apolyfluorinated polymer onto the glass fabric, heating the glass fabrichaving the polyfluorinated polymer thereon by subjecting it to a firstheat zone wherein the temperature is gradually increased from about 72F. to about 450 F. so that volatile material from the sizing on' theglass fibers is not entrapped therein and maintaining the temperature atabout 450 F. for about 12-18 hours, and subsequently subjecting theheated glass fabric to an additional heat zone ranging from about 640 F.to about 750 F. for approximately 15-35 hours, in order to sinter thepolyfluorinated polymer and to weave set the glass fabric, applying anorganosilicon material to the heat-treated glass fabric and drying theorganosilicon on the glass fabric.

2. The method as claimed in claim 1 in which the polyfluorinated polymeris polytetrafluoroethylene.

3. The method as claimed in claim 1 in which the thickened dispersion isapplied via knife coating to only one surface of the glass fabric.

4. A method for improving abrasion resistance and flammabilityresistance of glass fabric, said glass fabric comprising glass yarn,wherein said yarn comprises a multiplicity of bundles of glass fibers,which glass fibers are sized with a protective material, comprising thesteps of applying a thickened dispersion of very fine particles of apolyfluorinated polymer onto the glass yarn, drying the yarn, weavingthe yarn into fabric, heating the glass fabric by subjecting it to afirst heat zone wherein the tern erature is gradually increased fromabout 72 F. to about 4 0 F. so that volatile material from the sizing onthe glass fiber is allowed to escape therefrom maintaining thetemperature at about 450 F. for about 12-18 hours, and subsequentlysubjecting the heated glass fabric to an additional heat zone rangingfrom about 650 F. to about 750 F. for approximately 15-35 hours in orderto sinter the polyfluorinated polymer and to weave set the glass yarnsin the fabric, applying a lubricant to the heat treated glass fabric anddrying the lubricant on the glass fabric.

5. The method as claimed in claim 4 wherein the polyfluorinated polymeris polytetrafluoroethylene.

2. The method as claimed in claim 1 in which the polyfluorinated polymeris polytetrafluoroethylene.
 3. The method as claimed in claim 1 in whichthe thickened dispersion is applied via knife coating to only onesurface of the glass fabric.
 4. A method for improving abrasionresistance and flammability resistance of glass fabric, said glassfabric comprising glass yarn, wherein said yarn comprises a multiplicityof bundles of glass fibers, which glass fibers are sized with aprotective material, comprising the steps of applying a thickeneddispersion of very fine particles of a polyfluorinated polymer onto theglass yarn, drying the yarn, weaving the yarn into fabric, heating theglass fabric by subjecting it to a first heat zone wherein thetemperature is gradually increased from about 72* F. to about 450* F. sothat volatile material from the sizing on the glass fiber is allowed toescape therefrom maintaining the temperature at about 450* F. for about12-18 hours, and subsequently subjecting the heated glass fabric to anadditional heat zone ranging from about 650* F. to about 750* F. forapproximately 15-35 hours in order to sinter the polyfluorinated polymerand to weave set the glass yarns in the fabric, applying a lubricant tothe heat-treated glass fabric and drying the lubricant on the glassfabric.
 5. The method as claimed in claim 4 wherein the polyfluorinatedpolymer is polytetrafluoroethylene.